Die cutting machines, commonly known as clickers, are used for cutting blanks of sheet material for example, leather, paper, vinyl, etc. These machines have a stationary cutting block or bed upon which the stock or blank to be cut is spread and a movable striking element or arm by which a sharp edged die, placed on top the blank, is driven by impact through the blank.
As the commercial requirements and specifications (e.g. throughput) for die cutting machines increase, it is increasingly important that the machine be able to accurately sense the instant that the die is driven through the blank and contacts the supporting cutting block beneath the blank. This function is often accomplished by providing an electrically conductive path whereby the die, when it is completely through the blank stock, contacts the cutting block, and thereby completes an electrical circuit which causes the direction of travel of the striking pad to reverse. The cut stock is then removed and a new blank is positioned for cutting.
Several constructions have been used for the supporting cutting block. Most generally, the cutting block or pad comprises a rubber compound impregnated with carbon black to provide electrical conductivity. There have also been attempts lately to achieve electrical conductivity in the cutting block using a polypropylene-type compound, perhaps incorporating carbon black.
The literature also describes a cutting block having a laminated structure comprising a plurality of relatively insulating planar members interleaved with thin electrically conductive foil members. The entire assembly is bonded to form the laminated structure. This construction does not appear to have attained commercial viability, probably because of the relatively high cost of assembling the relatively complex and in part fragile structure. Thus, the thin foil material between insulating members may be prone to tearing and peeling; and the results of using the cutting block in the electrical circuit are unreliable, for example, where the die repetitively contacts the same area of the cutting block.
It is therefore an object of this invention to provide an electrically conductive cutting block which is reliable, which is simple to assemble, and which is low in cost. Other objects of the invention include providing a cutting block which is mechanically and adhesively secure, which can be constructed in any convenient size, which will not peel or rupture, and which can be made of substantially any convenient, suitably resistive and resilient, electrically insulating material.